The invention relates to edge protectors or "edge strips" used for preventing deposition of metals on edges of electrode plates in electrolytic cells.
Edge protectors, also referred to as "edge strips", commonly are utilized to prevent electrodeposition of recovered metal on "blank" electrolytic cell electrode plates (hereinafter, simply "electrodes" or "cathodes") in order to facilitate removal of thin (i.e., one-eighth of an inch) layers of metal from the cathodes. Typically, the cathode is lifted or "pulled" from the cell after the deposition of the layers or sheets of recovered metal on the opposite faces of a blank cathode is complete. The sheets of electrodeposited metal then are removed, for example by hand or by means of an automatic stripping machine which may strike the cathode while directing a high velocity jet of air at the edge of the cathode between the cathode surfaces and the thin sheets of electrodeposited metal being removed. It is important that the edges of the removed sheets of recovered metal be straight and non-jagged. Some conventional edge strips consist of extruded plastic U-shaped channels that rely on the "resilience" of the plastic to maintain a sufficient contact or "grip" with the surface of the blank electrode on which they are installed. Other known edge strips are held in place on the edge of a cathode by transverse pins extending through the sides of the edge strip and through the edge portion of the blank cathode. Such conventional edge strips do not prevent ingrowth of deposited metal between the edge strip and the edge surface portion of the cathode. The elasticity or resilience of the U-shaped channel of a typical prior edge strip is insufficient to press the opposed inner surfaces of the grooves formed by that U-shaped channel sufficiently tightly against the portions of the opposed surfaces along an edge of the cathode. Therefore, the prior edge strips do not effectively seal the portions of the opposed surfaces along the edge portions of the cathode from the electrolyte. To overcome this problem, expensive, complex equipment often is utilized to spray wax "beads" along the edges of plastic U-channel shaped edge strips after they are mounted on the edges of a blank cathode, in order to provide seals between the inner edges of the edge strips 3 shown in FIG. 1 and the main surfaces of the blank cathode 1.
FIG. 1 illustrates prior art edge strips 3 on a blank stainless steel cathode 1 used for electrolytic deposition of copper. Reference numerals 4 designate the above-mentioned sprayed-on wax bead. The edges of the wax beads 4 are quite un-uniform, which results in jagged edges of the layers of copper electrodeposited on the cathode 1. The process of spraying wax beads 4 is required every time cathode 1 is "pulled" from the electrolytic cell to remove the electrodeposited copper sheets. The wax spraying equipment is costly, as is the floor space required for it. The amount of time and labor required for spraying wax beads 4 every time the cathode is pulled is costly. The wax from the prior wax bead must be removed from the electrode and edge strips every time the electrode is "pulled". This is done with 190.degree. Fahrenheit water, overheating the edge strips and causing them to prematurely deteriorate. Furthermore, the jagged edges of the sheets of copper resulting from the un-uniform wax beads are unsatisfactory to copper buyers.
The state of the art for edge strips is indicated in "Edge Protection for Starter-Blanks and `Permanent` Matrix-Cathodes: A Systematic Approach to Solve Old Problems", by P. Berger, pages 469-479, and in U.S. Pat. No. 4,406,769 by Berger.
It would be highly desirable to provide an improved edge strip protector that avoids the need for expensive equipment utilized to spray the above-described wax beads to prevent electrolyte penetration between edge strips and blank cathodes.
Dual durometer extruding processes are known, and flexible dual durometer strips are commonly used around edges of refrigerator doors to seal the doors to refrigerator bodies. Use of dual durometer extruded structures to provide both structural rigidity and resilient contact to achieve an effective seal with a plate is not known, especially in the electrowinning industry.